| Objectives:To establish a three-dimensional finite element model of mandible and retrogression model of Bilateral Sagital Split Ramus Osteotomy(BSSRO),which will provide a basis for evaluation of the transverse displacement of proximal segment with different retrogression amounts and lingual split patterns under the loading of masticatory muscle force groups,and to examine the influencing factors that related to mandibular width.Materials and Methods:1?One dry dentate mandible with no cranial and maxillofacial deformities were selected and scaned by the spiral CT without interval,the scan data were saved in DICOM format and imported into software MIMICS and ANASYS.Then,a 3D model of mandible were constructed including the temporomandibular joint and teeth;2?Using the image segmentation function,a Bilateral Sagittal Split Ramus Osteotomy surgery consist of proximal and Distal Segments was performed,and different retrogression amounts and different lingual split patterns was simulated on the 3D models by the monocortical plate system,respectively;3?According to the attachment position and direction of the masticatory muscles,Bilateral superior region of the temporal bone and the teeth area were constrainted in all directions,simulating the masticatory muscle forces loading early stage on different Surgical model and Evaluating the transverse displacement of proximal segment.Results:1.A three-dimensional finite element model of mandible with temporomandibular joints and full dentition crowns was constructed,meanwhile four different retrogression surgery models were established which is a basis for further study of mandibular biomechanics after orthognathic surgery.2.Mandibular operation model of Hunsuck split style(F1)with different backward distances:M1(3mm retrogression of distal Segment)and M2(8mm retrogression of distal Segment),The results showed that the mean Widening distanceof proximal Segment were 2.955 mm and 3.490 mm,the transverse distance between the Go points increased 6.441 mm and 7.346 mm respectively,but there was no significance difference within two backward distances.3.Mandibular operation model with 8mm retrogression distance and different split style:F1(Hunsuck split style)and F2(Obwegeser split style),The results showed that the mean Widening distance of proximal Segment were 3.490 mm and 2.144 mm,the transverse distance between the Go points increased 7.346 mm and 5.212 mm respectively,but there was no significance difference within two split patterns.4.The displacement color scale of four 3D finite element models(F1-M1?F1-M2?F2-M1?F2-M2)all showed that the maximum transverse displacement distribution in the gonial area of the proximal segment,The transverse displacement distribution passed through the mandibular gonial area to condyle and coronoid process based on gradient image,beginning from the maximum value to the minimum value and from outward to inward.5.Comparison of the biomechanical characteristics between the original model and surgery model,besides coronoid process,simoid notch,Anterior border of ramus and mandibular angle,the fixation area of titanium plate and titanium screws also showed the Stress concentration obviously,which suggested that the fixed region was a weak area after maxillofacial surgery.Conclusion:1.With the help of reverse engineering software,the constructed mandible model can assist us to carry out all kinds of operation simulation and impact experiment conveniently and repeatly.2.The results of the study indicate that transverse displacement of the proximal segments widening most obvious after BSSRO surgery,The masticatory muscle groups and rigid internal fixation may play an important role on transverse displacement.3.The split pattern of rami mandibulae may Influence the widening of the proximal segments,which will work only in a short retrogression distance of distal segment. |
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